1. Technical Field
The present invention relates to an image forming apparatus and an image forming method of developing an electrostatic latent image by the use of toner in a state where a latent image carrier carrying the electrostatic latent image and a toner carrying roller carrying the toner are opposed to each other in a non-contact manner.
2. Related Art
As a technique for developing an electrostatic latent image by the use of toner, there is known a technique of so-called non-contact development method, where a latent image carrier for carrying an electrostatic latent image and a toner carrying roller for carrying the toner are opposed to each other with a gap therebetween and the electrostatic latent image is developed by causing the toner to fly through the gap (for example, see JP-2007-127800). In such a kind of image forming apparatus, toner having a volume average particle diameter of about 8 μm to about 10 μm has mainly been used until now. However, in order to achieve goals such as highly precise image, a high speed process, and a low fixing temperature, the toner is required to have a smaller particle size (for example, a volume average particle diameter of 5 μm or less).
It has recently been revealed that the toner with this smaller diameter behaves in a different manner from the toner with a larger diameter. For example, since an image force or the van der Waals force of the toner carrying roller on the charged toner having a small particle diameter is increased, it is difficult for the charged toner to fly from the toner carrying roller. Therefore, it is difficult to develop an image with a sufficient density. Moreover, since the toner having a small diameter and a small mass easily flies, the toner may become attached to the inside or the outside of the image forming apparatus or ground fogging may occur, thereby smearing the image to be formed.
Here, the lack of development density can be supplemented by increasing the amount of toner to be transmitted on the toner carrying roller or by strengthening an electric field to be generated in the gap between the latent image carrier and the toner carrying roller. However, even in this case, a problem arises in that too much toner flies. A goal of obtaining the sufficient development density is contrary to a goal of suppressing the toner flying to the inside and outside of the image forming apparatus or the ground fogging. Therefore, in order to achieve the smaller particle diameter of the toner while achieving these goals together, the known technique has to be improved.